Method and device for the production of a workpiece with internal toothing, in particular a hollow wheel

ABSTRACT

The invention relates to a method and an apparatus for producing a workpiece with internal toothing, especially an internal geared wheel, by using a cup-like preform (N) with a substantially cylindrical side wall (N 1 ) and a mandrel ( 5 ) with an external profile ( 6 ) according to the internal toothing to be produced, as well as with a forming tool which reduces the outside diameter of the cylindrical side wall during an advancing movement, as a result of which the material of the cylinder wall region flows into the external profile ( 6 ) of the mandrel ( 5 ). In accordance with the invention, the forming tool is configured as a drawing ring ( 14 ) ensuring the ironing of the cylinder wall region (N 1 ) during an advancing movement and that two tool elements act upon the preform (N) during the ironing, which tool elements produce axial compressive stresses in the cylinder wall region (N 1 ) of the preform. In accordance with the method, the reduction of the outside diameter occurs by ironing by means of a drawing ring and that during the ironing additional axial compressive stresses are applied onto the cylindrical side wall of the preform.

[0001] The invention relates to a method and an apparatus for producing a workpiece with internal toothing, especially an internal geared wheel, according to the preamble of the first claim. Such internal toothings are produced by means of flow turning. A cup-like preform is pressed according to DE 198 30 817 A1 by means of tapered rollers during an advancing movement against a clamping chuck which has the external profile of the internal toothing to be produced. Said preform is reduced in its diameter, with the preform rotating relative to the tapered rollers. The material of the cylinder wall region of the preform flows into the profile of the clamping chuck, as a result of which the inner profile of the workpiece is produced. The disadvantageous aspect is the high amount of flexing work which stresses the workpiece material during the flow turning and the thus inadequate quality of the produced internal toothing. A high local introduction of energy is connected with the flexing work which leads to energy losses. The external toothing as pictured therein frequently breaks off as a result of the high stresses on the clamping chuck. Moreover, the productivity of this method is relatively low despite a high need for machinery because only three to four parts per minute can be produced.

[0002] It is the object of the present invention to provide a method and an apparatus for an energy-saving production of a workpiece with internal toothing, especially an internal geared wheel, which ensures a substantial increase in the productivity at high quality of the internal toothing with a relatively simple constructional configuration of the apparatus.

[0003] This object is achieved by the features of the 1^(st) and 13^(th) claim. The apparatus for producing a workpiece with internal toothing, especially an internal geared wheel for a gearing, comprises a mandrel with an outside profile according to the internal toothing to be produced as well as a forming tool which reduces during an advancing movement the outside diameter of a cup-like preform, as a result of which material of the cylinder wall region flows into the outside profile of the mandrel. In accordance with the invention, a drawing ring is used as the forming tool which ensures ironing of the cylinder wall region during an advancing movement.

[0004] In the direction towards the lower side of the floor of the preform an axially movable counterholder is arranged in such a way that during the ironing it acts with a counterholding force on the lower side of the floor of the preform. The counterholder may comprise a circular pressure surface facing in the direction towards the lower side of the floor, which pressure surface substantially acts upon the entire floor region, or said counterholder may comprise a ring-like pressure surface which is adjusted to the width of the cylinder wall of the preform and is aligned essentially flush with the same and acts upon the edge region of the lower side of the floor of the preform.

[0005] An axially movable pressure punch is arranged in the direction towards the face surface of the cylindrical side wall in such a way that during the ironing it acts upon the face surface with a pressure force. The pressure punch can be moved during the ironing by a movement corresponding to the ironing length of the preform in the direction of the advancing movement of the drawing ring.

[0006] Advantageously, the axial stroke movement of the pressure punch as occurs during the ironing can be controlled depending on its pressure force. For this purpose the pressure punch is held in an axially movable fashion by means of a hydraulic piston.

[0007] The apparatus can advantageously be integrated in a hydraulic press consisting of a bedplate and a press ram. The mandrel is arranged in an axially fixed fashion on the bedplate and the press stamp is held on the mandrel in a manner so as to be axially displaceable by means of a hydraulic piston. The drawing ring is arranged on the press stamp in a preferably fixed manner and the counterholder is arranged thereon preferably in an axially movable fashion by means of a hydraulic piston. The pressure punch is preferably arranged as a cylindrical pressure sleeve. The distance of the pressure surface which is adjusted to the length of the preform to the face side of the mandrel can be adjusted by means of spacer rings for example.

[0008] For ejecting the workpiece the mandrel is held in a rotatable manner in the production of a helical gearing.

[0009] With respect to the method employed, the production of the workpiece with internal toothing occurs in such a way that a cup-like preform, comprising a floor and substantially cylindrical side walls, is reduced in its outside diameter by means of a mandrel having the external profile according to the internal toothing to be produced, so that the material of the cylinder wall region flows into the external profile of the mandrel. According to the invention, the reduction of the outside diameter occurs by ironing by means of a drawing ring. During the ironing the axial compressive stresses are applied onto the cylindrical side walls of the preform, so that the flow of material into the profile of the mandrel is promoted. The axial compressive stresses are preferably applied by a pressure punch acting upon the face side of the cylinder wall. A counterholder acts simultaneously on the lower side of the floor in order to avoid deformations in the floor region and to apply a counterholding force. The counterholding force of the counterholder and the force of the pressure punch should be controllable with respect to each other in such a way that during the entire ironing process a flow of material is ensured in the radial direction to completely fill the shape of the mandrel.

[0010] During the ironing, the pressure punch carries out an axial stroke movement according to the ironing length of the preform in the direction of the advancing movement of the drawing ring which is controlled depending on its pressure force.

[0011] The invention allows for the first time producing internally geared workpieces in high quality on a conventional press in an energy-saving manner. The productivity can be increased by four to six times in comparison with flow-turning.

[0012] The invention is now explained in closer detail by reference to an embodiment and the pertinent drawings, wherein:

[0013]FIG. 1 shows an apparatus with an inserted preform before the ironing;

[0014]FIG. 2 shows an apparatus during the ironing;

[0015]FIG. 3 shows an apparatus with an inserted preform and material overflow in the counterholder before the ironing;

[0016]FIG. 4 shows an apparatus according to FIG. 3 during the ironing;

[0017]FIG. 5 shows an apparatus after ending the ironing with an additional calibrating pressure and additional material overflow at the end of the cylindrical edge of the workpiece.

[0018]FIGS. 1 and 2 show the principal configuration of the apparatus as integrated in a press. The lower part 2 of the tool is arranged on the bedplate 1, which lower part comprises a first hydraulic piston 3. The mandrel 5 is fastened in an axially fixed manner via a stamp 4 to the lower part 2 of the tool, which mandrel has an external profile 6. An ejector 7 extends in the middle of the stamp 4 and the mandrel 5. The pressure punch 9 which is arranged as a pressure sleeve is held in an axially movable way on the hydraulic piston 3 via an adapter 8. The axial position of the pressure punch 9 can be changed via spacers 10 which can be attached between the adapter 8 and the pressure punch 9. The upper part 11 of the tool is arranged on the press ram P and comprises a counterholder 12 which is axially adjustable via a second hydraulic piston 13. The drawing ring 14 is fastened in a fixed manner on the press ram via an adapter 15.

[0019] According to FIG. 1 the cup-like preform N was placed over mandrel 5 with the cylindrical edge N1 facing downwardly, so that the face surface N2 faces in the direction towards the press stamp 9 and the lower side of floor N3 faces in the direction towards the counterholder 12. According to the method, the hydraulic piston 13 moves the counterholder 12 in the direction towards the lower part of the tool until the counterholder 12 rests on the lower side of floor N3.

[0020] The drawing ring 14 which is arranged in a fixed fashion on the press ram P moves in the pre-stroke with the press ram P in the direction towards the bedplate 1. At the same time, the first hydraulic piston 3 is pressurized and presses the press stamp 9 with the force Fl against the face surface N2 of the preform N (FIG. 2). At the same time, the counterholder 12 acts a counterholding force F2 on the floor of the cup. During the ironing the pressure punch 9 performs a movement in the direction of the pre-stroke of the drawing ring 14 according to the drawing of the preform N, with the pressure acting upon the wall N2 being maintained by the forces F1 and F2. As a result of the compressive stresses produced in the workpiece wall N2, the flow of material is promoted, so that the material flows reliably into the profile 6 of the mandrel 5. An outstanding quality of the internal toothing is thus achieved. After the completion of the ironing, the upper part 11 of the tool moves upwardly and the workpiece is removed form the mandrel 5 by means of the ejector 7, with the same being held in a rotatable fashion in the case of a helical gearing.

[0021] In order to allow excessive material to flow off and to avoid overloading the tool it is possible according to FIGS. 3 and 4 to provide a material overflow 12.2 in the counterholder 12. The counterholder 12 comprises a thrust member 12.1 in the direction towards the workpiece N, which member is also reduced in its diameter in the direction towards the workpiece N, thus producing a gap between the thrust member 12.1 and adapter 15 into which the excessive material can flow and which is thus used as a material overflow 12.2.

[0022] According to FIG. 5 it is also possible, in addition to the material overflow 12.2 as provided for in FIGS. 3 and 4, to arrange a further material overflow 12.3 at the end of the cylindrical wall. The gap between the outside diameter of the pressure punch 9 and the inner diameter of the drawing ring 14 can be used for this purpose.

[0023] It is further advantageous when at the end of the forming process an increased axial pressure for calibration is exerted in order to achieve a better filling and a higher excessive material can flow off as described above. After cylinder 3.1 is situated in its lowermost position. The increased pressure can now be applied in such a way for example that the pressure punch 9 via an intermediate piece Z which comprises a thread G on its outside diameter and is connected above with a ring follower G1 which on its part rest on the cylinder 3.1 and thus on the bedplate 1 via the lower part 2 of the tool. 

1. An apparatus for producing a workpiece with internal toothing, especially an internal geared wheel, by using a cup-like preform (N) with a substantially cylindrical side wall (N1) and a mandrel (5) with an external profile (6) according to the internal toothing to be produced, as well as with a forming tool which reduces the outside diameter of the cylindrical side wall during an advancing movement, as a result of which the material of the cylinder wall region flows into the external profile (6) of the mandrel (5), characterized in that the forming tool is configured as a drawing ring (14) ensuring the ironing of the cylinder wall region (N1) during an advancing movement and that two tool elements act upon the preform (N) during the ironing, which tool elements produce axial compressive stresses in the cylinder wall region (N1) of the preform.
 2. An apparatus as claimed in claim 1, characterized in that a first tool element in form of an axially movable counterholder (12) is arranged in the direction towards the lower side of the floor (N3) of the preform (n) in such a way that it acts during the ironing with the drawing ring upon the lower side of the floor (N3) of the preform (N) with a counterholding force (F2).
 3. An apparatus as claimed in claim 2, characterized in that the counterholder (12) comprises a circular pressure surface facing in the direction towards the lower side of the floor (N3) and acts substantially on the entire floor region.
 4. An apparatus as claimed in one of the claims 1 to 3, characterized in that the counterholder (12) comprises a ring-like pressure surface facing in the direction towards the lower side of the floor (N3), which pressure surface is adjusted to the width of the cylinder wall region (N1) of the preform (N) and is substantially aligned flush with the same and acts upon the edge zone of the lower side of the floor of the preform.
 5. An apparatus as claimed in one or several of the claims 1 to 4, characterized in that in the direction towards the face surface (N2) of the cylinder wall region (N3) of the preform the second tool element in the form of an axially movable pressure punch (9) is arranged in such a way that it acts upon the face side (N2) with a force (F1) during the ironing.
 6. An apparatus as claimed in one or several of the claims 1 to 5, characterized in that the pressure punch (9) is axially movable during the ironing process by an axial movement corresponding to the ironing length of the preform (N) in the direction of the advancing movement of the drawing ring (14).
 7. An apparatus as claimed in claim 6, characterized in that axial movement of the pressure punch (9) occurring during the ironing can be controlled depending on its counterholding force (Fl).
 8. An apparatus as claimed in one or several of the claims 1 to 7, characterized in that the pressure punch (14) is held in an axially movable way via a hydraulic piston (3).
 9. An apparatus as claimed in one or several of the claims 1 to 8, characterized in that it is integrated in a press consisting of a bedplate (1) and a press ram (P) in such a way the mandrel (4) is axially fixed to the bedplate (1) and the pressure punch (9) is held on the mandrel (4) in a manner so as to be axially displaceable by means of the hydraulic piston (3), and that the counterholder (12) is axially movable in a pressurizable manner on the press ram (P) and the drawing ring (14) is arranged so as to be fixedly fastened.
 10. An apparatus as claimed in one or several of the claims 1 to 9, characterized in that the pressure punch (9) is arranged as a cylindrical pressure sleeve.
 11. An apparatus as claimed in claim 10, characterized in that the distance of the pressure surface of the pressure punch (9) from the face surface of the mandrel (5) which can be adjusted to the length of the preform (N) can be set by means of spacer rings (10).
 12. An apparatus as claimed in one of the claims 1 to 11, characterized in that the mandrel (5) is held rotatably for ejecting the workpiece (N).
 13. An apparatus as claimed in one or several of the claims 1 to 12, characterized in that an ejector (7) which runs axially along in the mandrel (5) is held in a rotatable fashion.
 14. An apparatus as claimed in claim 1, characterized in that a material overflow is arranged on one side or either side at the end of the workpiece.
 15. An apparatus as claimed in claim 14, characterized in that a material overflow (12.2) is arranged in the counterholder (12).
 16. An apparatus as claimed in claim 15, characterized in that a material overflow is arranged in the adapter (8) in which the pressure punch (9) is held.
 17. A method for producing a workpiece with an internal toothing, with a cup-like pre-form with a floor and a substantially cylindrical side wall is reduced in its outside diameter by means of a mandrel which comprises the outside profile according to the inner toothing to be produced, so that the material of the cylinder wall region flows into the outside profile of the mandrel, characterized in that the reduction of the outside diameter occurs by ironing by means of a drawing ring and that during the ironing additional axial compressive stresses are applied onto the cylindrical side wall of the preform.
 18. A method as claimed in claim 17, characterized in that the axial compressive stresses are produced by two tool elements which act on both sides on the region of the cylindrical side walls.
 19. A method as claimed in one or several of the claims 17 to 18, characterized in that during the ironing a first tool element in the form of a counterholder acts with a counterholding force (F2) upon the lower side of the floor and a second tool element in the form of a pressure punch acts with a force (F1) upon the face side of the cylindrical side wall.
 20. A method as claimed in one or several of the claims 17 to 19, characterized in that during the ironing the pressure punch performs an axial stroke movement corresponding to the ironing length of the preform in the direction of the advancing movement of the drawing ring.
 21. A method as claimed in claim 20, characterized in that the axial stroke movement occurring during the ironing is controlled depending on its force F2.
 22. A method as claimed in one or several of the claims 17 to 21, characterized in that the counterholder force (F2) of the counterholder and the force (F1) of the pressure punch are mutually controllable in such a way that during the entire ironing process a material flow is ensured in the radial direction for the purpose of completely filling the contour of the mandrel.
 23. A method as claimed in one or several of the claims 17 to 22, characterized in that after terminating the ironing an increased axial pressure is exerted for calibrating the workpiece.
 24. A method as claimed in one or several of the claims 17 to 23, characterized in that during the ironing and/or during the application of the calibrating pressure excessive material flows into the material overflows. 